1. Field of the Invention
The present invention refers to a rotary die cutter unit with rapid die connection, for cardboard shapes for boxes, that is part of a shape-production line, that prints, feeds and cuts the shapes themselves through such rotary die cutter unit, before cleaning, stacking and placing them on pallets to ship them.
2. Description of Prior Art
Various types of rotary die cutter units are known in the art, comprising a rotary die-holding cylinder, on which a wooden die with inserted blades is mounted to cut and shape the cardboard, according to the type of box to be produced. The major problem for all known devices built so far has been prearranging an effective connection between the die-holding cylinder and the die, that guarantees an easy and quick replacement, contact efficiency between the two parts for shape die-cutting accuracy, and optimal operating life.
In addition to the old type of connection with common screws, that surely is not the optimum solution due to its cumbersome and long operations, above all if frequent die changes occur, the most recent technical solutions are those disclosed in European Patent No. 0 384 161 in the name of Martin and in Italian Patent Application No. TO92A000177 assigned to the same Assignee of the present invention. The solution described in European Patent No. 0 384 161 shows connecting half-circumferences on the die that come into engagement with grooves on the cylinder and are kept engaged by longitudinal bars pushed against them; however, in addition to sliding problems for the bars in dusty environments, this solution has a problem dealing with connection accuracy, that is not uniform if, due to any reason, the bar is not able to couple all half-circumferences on the die: since the bar has a single working stroke, connection misalignments, that are frequent in harsh environments like the cardboard cutting ones, are transmitted on the whole bar impairing contact accuracy between die and cylinder.
On the other hand, the solution described in Italian Patent Application No. TO92A000177, though solving the previously mentioned problems, is difficult to realize, due both to costs and to the great number of connecting devices used.